Electroextraction des protéines des microrganismes photosynthétiques/Electroextraction of proteins from photosynthetic microorganisms

The demand for sustainable protein sources to feed the global population is increasing as the population is anticipated to reach 9.7 billion by 2050. Therefore, a search for alternative proteins sources to meat ones is necessary. A promising alternative is microalgae due to their high protein content while having a reduced environmental impact compared to animals and plant proteins. Beside the challenge constituted by consumer acceptance of these alternative protein production from microalgae still require the development of methods that will enable to improve the extraction of proteins. Conventional protein extraction methods, such as enzymatic hydrolysis and biochemical processes, are laborious, time-consuming, and may require the use of solvents. Extraction methods using physical treatment that are all destructive for the biomass, that needs to be production at each extraction cycle, which is time and energy consuming. Alternative extraction processes, called biocompatible extraction or milking, have been proposd for rendering extraction more friendly from the environmental and economic point of views. In this frame, Justine MARCHAND and Benoît SCHOEFS (team MIMMA) of BiOSSE develop processes aiming at extracting proteins without killing the biomass using different means including biocompatible pulsed electric field (bcPEF). bcPEF are reversible PEF i.e. that keeps cells alive. The thesis would be part of a research programme financed by France2030 and involving several academic and industrial partners.

Assumptions and questions: One of the goals of the work has been to understand how microalgae respond to the repeated extraction of a significant proportion of their internal soluble proteins triggered by repetitive bcPEF. The proposed work lies on 5 hypotheses : H1-bcPEF-induced stress is moderate and the microalga recovery is fast; H2- the cellular protein quota (QProt) is reconstituted rapidly and the extraction yield does not vary significantly between 2 extractions; H3-cell division is not severely affected by bcPEF; H4: the composition in terms of types of proteins is constant and the extracted proteins are not damaged between 2 extractions; H5: protein recovery from the extracting medium is efficient. The questions to be answered corrrespond to these 5 hypotheses Q1- what is the level of permeability and the microalgal stress level induced by bcPEF; Q2-how fast is the de novo protein accumulation between 2 bcPEF; Q3-how bcPEF impact cell division rate and Q4-what are the identity and the state of the extracted proteins.

The main steps of the thesis and scientific procedure: The main steps are (1) establishing the culture of the different taxa (Arthrospira platensis, Chlorella vulgaris, and Tetraselmis chui) and (2) optimizing the conditions allowing the best protein extraction while preserving cell viability. Using these conditions, the answers to the five groups of questions mentionned above will be obtained: A1-evaluating the level of permeability and the microalgal stress level induced by bcPEF; A2-establishing the kinetics of de novo protein accumulation between 2 bcPEF; A3-evaluating the impact of bcPEF on cell division rate and A4-determining the quality and the identity of the extracted proteins

Methodological and technical approaches considered: Axenic culture of photosynthetic microorganisms will be tested: Arthrospira platensis, Chlorella vulgaris, and Tetraselmis chui. The project is organized in 3 WPs: WP1-Electroporation and cell responses after 1 PEF: permeability measurements (flow cytometry, fluorescence microscopy), quantification and identification of the released proteins. The protein analyses will be performed with the help of PROTEOTOUL plateforme, stress level and impact of the protein unbalance on metabolic changes (transcriptomics, proteomics, spectroscopies, oxidative stress measurements) → bcPEF operating conditions and relaxation time for bcPEF treatment, biomass/protein production modelling and small scale cultivation adjustments (nutrients, dilution and lighting) considering the extracted proteins (A1), WP2–Repetitive extraction: morphologic changes, division rate, identification, quantitative and qualitative analyses of the released proteins by mass spectrometry (PROTEOTOUL), viability→ repetitive extraction operating conditions, biomass/protein production modelling and small scale cultivation adjustments (nutrients, dilution and lighting) (A2-A4)

Scientific and technical skills required by the candidate: The project is multidisciplinary. Knowledge in algal culture, physiology, biochemistry, biophysics, electroextraction, flow cytometry, bioinformatics will be good point. Autonomy, knowledge of English, mobility

As part of a new project ‘alternative PROteinS : Production, ExtraCTion, dryIng, Ingredients Valorisation, for the improvement of protEins Sustainability in human diet’ (PROSPECTIVES) led by the University of Dijon, Le Mans University, is recruiting a PhD student. This multidisciplinary project will contribute to the establishment of biocompatible electroextraction as a new biotechnological tool for the extraction of proteins from microalgae. The PhD work is led by Justine Marchand and Benoît Schoefs. .

The doctoral student will be a member of the « Metabolism, bioengineering of molecules and applications of microalgae » (MIMMA) team of the « Mer Molécules Santé » laboratory at Le Mans University. The team is interested in the mechanisms of reorientation of the carbon metabolism of microalgae in response to stress and in applications in the field of blue biotechnology. The ‘PROSPECTIVES’ program presents both fundamental and applied aspects.

Les candadates devraient démontrer une exêrience dans les différents domaines

Culture de microalgues

Biologie moléculaire, biochimie et physiologie des microalgues

Autonomie, connaissance de l’anglais, mobilité

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The candidates sould demonstrate an exêrience in the different fields

Microalga culture

Molecular biology, biochemistry and physiology of microalgae

Autonomy, knowledge of English, mobility